Method and apparatus for fiber optic signature recognition

ABSTRACT

A method and apparatus is disclosed for use in fiber optic signature recognition to analyze buried optical fiber to identify a non-threat area along a fiber route and to discontinue monitoring for disturbances along that area of the cable route. The technique includes determining the location of the zone of non-threatening disturbances from comparing an optical signal to the representation of a prearranged optical signal identified as friendly. Once a zone of non-threatening disturbances is identified, all subsequent disturbances in that zone are considered friendly. Cable monitoring is discontinued in the identified zone of non-threatening disturbances so as to avoid monitoring fiber cable when permitted workers are in the area.

FIELD OF THE INVENTION

The present invention relates generally to techniques for detectingground vibrations caused by disturbances along a buried optical fiber.More particularly, the present application relates to using aprearranged signal which is understood as a non-threat to the system todetermine a zone of non-threatening disturbances and to discontinuemonitoring or ignore optical signals along that portion of the cableroute.

BACKGROUND OF THE INVENTION

U.S. Pat. No. 5,778,114 (the “114 patent”), assigned to the sameassignee as the present application and incorporated by referenceherein, discloses a system that allows fiber optics to be used as asensor and that can detect signals/activities along a cable right ofway. This system operates by sending pulses of light signals down afiber of a telecommunications plant, and detecting return signalsgenerated along the fiber path. This will allow detection of variousvibrations and frequency patterns generated in the vicinity of the fibercable. These return signals are broken down into discrete sections alongthe cable and are analyzed to determine the type and location of thedisturbance causing the vibration. Once a disturbance is detected thesystem will alert personnel to analyze the disturbance.

The '114 patent discloses a fiber sensing system that allows monitoringa fiber cable route for disturbances along its path. This device candetect personnel walking, running, digging, and vehicles, etc. along thecable right of way. This system will operate via the fiber and can lookat fiber in 20 meter increments over a 25 mile span. This deviceoperates on the same principle as an OTDR fiber test set. Disturbancesalong the fiber cable can be detected and analyzed by the system.Disturbances can be identified based on known patterns or frequenciesgenerated by the disturbance. For example, a person running and a personwalking can be distinguished from each other based on the patterngenerated from monitoring the fibers.

Often personnel work in the area of the fiber cable. Those personnel maybe authorized maintenance personnel that are aware of the undergroundfiber cable, or may be unauthorized personnel that present a threat tothe underground plant. When a disturbance is detected, a fiber ownermust investigate each disturbance. In the case of a threat beingdetected, a crew is sent to the site to investigate. False alarms arecost intensive and involve expensive manual overhead. What is needed isa way to distinguish non-threat disturbances from disturbances whichreally threaten the cable so to reduce the number of false alarms ininvestigating cable threats. If there is a legitimate disturbance suchas scheduled maintenance near a cable route, this disturbance is anon-threat and can be ignored. When monitoring a cable route, if thereare workers present in an area, there is a need to identify them as anon threat to the system.

SUMMARY OF THE INVENTION

The present invention addresses the needs described above by providing amethod and apparatus for identifying a zone of non-threateningdisturbances along a buried optical fiber cable by comparing adisturbance signal along a fiber with a prearranged set of disturbancesand discontinuing monitoring of this zone of non-threateningdisturbances. The system does not require an exact match of theprearranged signal to the optical signal generated from the disturbance.It uses an approximation algorithm that takes into account environmentalconditions and matches based on a close similarity. For example, soilconditions may be more packed in some areas affecting the low frequencyground vibrations. The match in this case would occur for a range ofsoil conditions.

The invention may be used as a security device to protect a perimeter byburying the cable along a perimeter and distinguishing threatening andnon-threatening disturbances.

One embodiment is a method of identifying a zone of non-threateningdisturbances along a buried optical fiber cable. The method comprisesthe steps of receiving an optical signal including a light patterncaused by a low frequency ground vibration at a location along thefiber; comparing the received signal to a representation of aprearranged optical signal; and, if the received signal and theprearranged signal match, identifying the zone of non-threateningdisturbances at the location.

The method may further include the steps of receiving a second opticalsignal including a light pattern caused by a second low frequency groundvibration at a location along the fiber; determining a location of thesecond vibration; and if the location of the second vibration is in thezone of non-threatening disturbances, then determining that the secondvibration is non-threatening.

The method may include the step of identifying the zone ofnon-threatening disturbances. The method may include discontinuingmonitoring optical signals from the zone.

The method may further comprise the step of introducing the lowfrequency ground vibration using a crystal controlled oscillator. Theoscillator in that method may be a motorized rod. The oscillator in thatmethod may be a metal plate placed on the ground. The crystal controlledoscillator may be attached to a piece of equipment such that thevibration is transmitted into the ground though the equipment.

The oscillator in that method may further include a rechargeable batterypower supply for operating the motor driven rod.

A second embodiment of the invention is an apparatus for distinguishingground vibrations caused by threatening and non-threatening disturbancesalong an optical fiber cable. The apparatus for distinguishing groundvibrations includes a light source for introducing a beam of light intothe optical fiber cable; a detector for receiving an optical signal fromthe optical fiber cable, the signal including light from the introducedbeam having characteristics caused by the ground vibrations; a processorconnected for receiving information from the detector; memory mediaconnected to the processor and containing a representation of aprearranged optical signal; memory media connected to the processor andcontaining a set of executable instructions that, when executed, causethe processor to receive an optical signal from the optical fiber cable,compare the signal with the representation of a prearranged opticalsignal, and, if the optical signal matches the prearranged opticalsignal, identify a zone of non-threatening disturbances at the location.

The apparatus may further comprise executable instructions furthercausing the processor to receive a second optical signal including alight beam having characteristics caused by a second low frequencyground vibration at a location along the fiber; to determine a locationof the second vibration; and, if the location of the second vibration isin the zone of non-threatening disturbances, then to determine that thesecond vibration is non-threatening.

The apparatus may further include the step of identifying the zone ofnon-threatening disturbances includes discontinuing monitoring opticalsignals from the zone.

The apparatus may further include a crystal controlled oscillator forintroducing the low frequency ground vibration. The oscillator may be amotorized rod. The oscillator may be a metal plate placed on the ground.The crystal controlled oscillator may be attached to a piece ofequipment such that the vibration is transmitted into the ground thoughthe equipment. The oscillator may further include a rechargeable batterypower supply for operating the motor driven rod.

A third embodiment of the invention is a method of identifying a zone ofnon-threatening disturbances along a buried optical fiber cable. Themethod comprises the steps of receiving a first optical signal includinga light pattern caused by a first low frequency ground vibration;determining that the first optical signal is a prearranged signalindicating non-threatening disturbances; determining a location of thefirst low-frequency ground vibration along the buried optical fiber;receiving a second optical signal including a light pattern caused by asecond low frequency ground vibration at a location along the fiber;determining a location of the second low-frequency ground vibrationalong the buried optical fiber; and if the locations of the first andsecond low-frequency ground vibrations are within a predetermineddistance, identifying the second low-frequency ground vibration as beingcaused by a non-threatening disturbance.

The method may include the step of determining that the first opticalsignal is a prearranged signal indicating non-threatening disturbancescomprises comparing the first optical signal to a representation of aprearranged optical signal.

The method may further comprise the step of introducing the first lowfrequency ground vibration using a crystal controlled oscillator. Thecrystal controlled oscillator in the method may be attached to a pieceof equipment such that the vibration is transmitted into the groundthough the equipment.

A fourth embodiment of the invention is a method of monitoring aperimeter for disturbances. The method comprises the steps of burying anoptical fiber cable along the perimeter; receiving an optical signalincluding a light pattern caused by a low frequency ground vibration ata location along the fiber; comparing the received signal to arepresentation of a prearranged optical signal; and recognizing theoptical signal as caused by ground vibrations from a non-threateningsource based on the comparing of the received signal to a representationof a prearranged optical signal.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic representation of a disturbance device andmonitoring system according to one embodiment of the invention.

FIG. 2 is a schematic representation of a disturbance creator accordingto one embodiment of the invention.

FIG. 3 is a schematic representation of a disturbance creator accordingto a second embodiment of the invention.

FIG. 4 is a flow chart depicting a method according to one embodiment ofthe invention.

DESCRIPTION OF THE INVENTION

The inventors have developed a method and apparatus for conductingimproved fiber optic signature recognition. The apparatus and methodreduce the overhead of monitoring the cable run in its entirety, byidentifying sections or zones that are under authorized maintenance. Inthose sections, active monitoring is not required or disturbances areignored. The invention includes an oscillator box mechanically connectedto the ground for generating known prearranged disturbance vibrations inthe area where authorized maintenance is taking place. These prearrangedvibrations are picked up by a Fiber Threat Analysis System (FTAS) andrecognized as a non threat. A location of the known vibration isdetermined, and the system establishes a zone of non-threateningdisturbances based on that location. In the zone further disturbancesmay be either ignored or not monitored.

In one version of the invention the oscillator box includes a metallicbox with a vibrating rod that will tamp out signals or vibrations intothe ground at a known rate and pattern. Another version of the apparatuscan be attached to a piece of construction equipment such that thevibration can be transmitted into the ground though the wheels or tracksof the vehicle. A third version of the apparatus sits on a metal plateon the ground. The unit includes a motor under the control of a crystalto generate an oscillatory frequency. The unit has a rechargeablebattery power supply that operates the motor driven parts.

The method may also be used in perimeter monitoring to secure a border.The method monitors disturbances along a fiber cable that is buried inthe ground along a border perimeter. Disturbances are detected andnotifications sent to a monitoring system to keep the area secure.

An apparatus according to one embodiment of the invention includes thecrystal controlled vibrator rod, a plurality of controls for operation,a battery box, a fiber cable and a fiber monitoring system. Thisapparatus provides a set of prearranged disturbances from crystalcontrolled oscillations and has them vibrate into the ground from theoscillator. FIG. 1 shows an embodiment of schematic representation of adisturbance generating device and monitoring system according to oneembodiment of the invention.

The oscillator device 100 includes a vibrating rod 110 that is insertedinto the ground 127. A plurality of controls for operation 115,including a crystal, is embedded in the oscillator device 100. A batterybox 125 is a rechargeable battery power supply that operates the motordriven vibrating rod 110. The battery box 125 may be connected to avehicle for power.

Signals in the form of low frequency ground vibrations 120 from thevibrator rod 110 enter the ground 127 around the fiber cable 130. Thevibrating rod can be inserted into the ground so that it generates astrong enough signal to create a known disturbance to the fiber cable.The rod is placed in the ground by a maintenance crew, for example,before beginning work near the fiber cable 130. The vibrating rod 110tamps out a defined pattern that is recognized by the fiber analysissystem 135. The vibration pattern is controlled via a frequency patterngenerated by the crystal. This crystal holds the vibration to a knownfrequency pattern, making the vibration identifiable. These identifiablevibration patterns are designed to match the prearranged signals storedin the fiber analysis system.

The FTAS includes a memory such as data storage 136 containingrepresentations of the known, prearranged signals. The FTAS alsoincludes a processor 137 for executing steps according to methods of theinvention. The memory may also contain instructions for executing thosemethods of the invention.

The fiber analysis unit does not require an exact match of signals. Forexample, the low frequency ground vibration signal from the oscillatordevice may vary dependent on soil conditions. There are areas where thesoil may be tightly packed or other areas where the soil is somewhatlooser. The fiber analysis unit does the match taking environmentalconditions into account. The fiber analysis unit 135 detects vibrationon cable 130 and if it is determined to be a match, labels it a nonthreat to the cable 130.

A low frequency vibration ground disturbance creator shown in the fieldaccording to another embodiment of the invention is shown in FIG. 2.

Two authorized maintenance vehicles 205 are shown working the areaaround the cable 230. They are excavating the ground 227 as duringregular maintenance procedures. Each maintenance vehicle 205 hasattached to it a crystal controlled oscillator 200. The oscillator 200is connected to the ground 227 in the immediate vicinity of the cable230. The cable is connected to the (FTAS) Fiber Threat Analysis System235. The FTAS 235, upon recognizing vibrations from the oscillator 200as the prearranged vibration pattern, sends messages to the serviceterminal 245 as a notification that the disturbance is a non threat.

Scheduled maintenance work on the cable 230 is being performed bytrusted contractors 205. The maintenance vehicles 205 carry anoscillator 200 to identify them as non-threats. As the contractors 205work, the oscillator 200 generates a known disturbance into the groundidentifying these vibrations as friendly thus avoiding the need tomonitor this section of the cable for threats. The known vibration ispicked up by the FTAS 235 which identifies the vibration as a non threatand sends the notification of non threat 240 to the monitoring device245.

The method furthermore reduces the need for monitoring areas wherefriendly personnel are working in the area of the fiber cable. It alsorequires no special knowledge of the monitoring organization; forexample, human monitors do not need to understand disturbance signals orthe signal recognition system. The method greatly reduces the overheadin monitoring a cable route and the time to determine that a disturbanceis of a non threatening nature.

FIG. 3 depicts the oscillatory device situated on a metal plate placedon the ground. Oscillations are generated in the oscillatory box 300.The vibrations travel into the metal plate 310 and directly vibrate intothe ground 320. These signals 330 travel as low frequency vibrationsthrough the ground 320 where they contact the fiber cable 340.

An exemplary method according to one embodiment of the invention isdescribed with reference to the flow chart of FIG. 4. In a first step400 of the method, a first optical signal is received including a lightpattern caused by a first low frequency ground vibration.

The following two steps 410 and 420 are performed by the fiber analysisunit. The fiber analysis unit determines that the first optical signalreceived is a prearranged signal indicating a non-threat 410. Thatdetermination is made in a preferred embodiment by comparing thereceived light pattern to stored signal representations. It thendetermines the location for the first low frequency ground vibration420. The location may be determined for example, using the techniquesdescribed in the '114 patent, discussed above.

The next two steps 430 and 440 process a second received signal. Thefiber analysis unit received a second optical signal 430 along thefiber. It then determines the location of the second signal 440.

The fiber analysis unit now has the information it needs to determine ifthe locations of the 2 received signals are close 450. If the signalsare in the same location of the fiber cable, the second signal islabeled as non-threatening. In so doing the fiber analysis unit haseffectively defined a zone of non-threatening disturbances at thelocation. This allows the fiber analysis system to monitor other areasof the fiber cable, and ignore this area as a friendly area.

The foregoing Detailed Description is to be understood as being in everyrespect illustrative and exemplary, but not restrictive, and the scopeof the invention disclosed herein is not to be determined from theDetailed Description, but rather from the claims as interpretedaccording to the full breadth permitted by the patent laws. For example,while the method of the invention is described herein with respect to adisturbance device attached to a piece of construction equipment orplaced on or in the ground, the method and apparatus of the inventionmay be instead embodied by any apparatus that imparts vibrations intothe ground. It is further noted that the invention is not limited to usewith current technology fiber, as described in this specification, butcan be used with any fiber cable technology existing today or developedin the future. It is to be understood that the embodiments shown anddescribed herein are only illustrative of the principles of the presentinvention and that various modifications may be implemented by thoseskilled in the art without departing from the scope and spirit of theinvention.

1. A method of identifying a zone of non-threatening disturbances alonga buried optical fiber comprising: inputting a light into a first end ofthe buried optical fiber; receiving a first optical signal from thefirst end of the buried optical fiber created by a first low frequencyground vibration received by the buried optical fiber; identifying thelocation along the buried optical fiber where the first low frequencyground vibration was received; analyzing the received first opticalsignal using an approximation algorithm comprising: adding environmentalcondition variables to the received first optical signal forming aconditioned first optical signal; comparing the conditioned firstoptical signal with a set of prearranged optical signals, theprearranged optical signals corresponding to predefined low frequencyground vibration patterns; if the comparison determines that theconditioned first optical signal matches one prearranged optical signalfrom the set of prearranged optical signals, identifying the first lowfrequency ground vibration location as a non-threatening disturbance;and if the comparison determines that the conditioned first opticalsignal does not match one prearranged optical signal from the set ofprearranged optical signals, identifying the first low frequency groundvibration location as a threatening disturbance.
 2. The method accordingto claim 1 further comprising: receiving a second optical signal fromthe first end of the buried optical fiber created by a second lowfrequency ground vibration received by the buried optical fiber;identifying the location along the buried optical fiber where the secondlow frequency ground vibration was received; and identifying the secondlow frequency ground vibration as a non-threatening disturbance when thesecond low frequency ground vibration location is within a predetermineddistance of the first low frequency ground vibration location.
 3. Themethod according to claim 2 further comprising: introducing a lowfrequency ground vibration into the ground using a vibrator; andcontrolling the vibrator to produce a low frequency ground vibrationsignature that matches one or more of the set of prearranged opticalsignals.
 4. The method of claim 3 further comprising attaching thevibrator to a piece of equipment such that the vibrator's low frequencyground vibration signature is transmitted into the ground where thepiece of equipment contacts the ground.
 5. The method of claim 1 whereinthe environmental condition variables condition the received firstoptical signal according to ground characteristics such as packed,loose, wet and dry soil at the location of the first low frequencyground vibration.
 6. A system for distinguishing ground vibrationscreated by threatening and non-threatening disturbances along a buriedoptical fiber comprising: a light source configured to introduce a beamof light into a first end of the buried optical fiber; a detectorconfigured to receive optical signals from the first end of the buriedoptical fiber, each received optical signal created by low frequencyground vibrations received by the buried optical fiber; a processorcoupled to the detector and configured to receive the received opticalsignals; and a data store coupled to the processor configured to containone or more representations of prearranged optical signals correspondingto predefined low frequency vibration patterns and a set of executableinstructions that when executed cause the processor to identify thelocation of low frequency ground vibrations associated with a receivedoptical signal, analyze the received optical signal using anapproximation algorithm that adds environmental condition variables tothe received optical signal forming a conditioned optical signal,compare the conditioned optical identify the low frequency groundvibration location corresponding to the matched conditioned opticalsignal as a non-threatening disturbance when a comparison determinesthat the conditioned optical signal matches one prearranged opticalsignal.
 7. The system according to claim 6 wherein the processor isfurther configured to compare the location of a low frequency groundvibration associated with one received conditioned optical signal withthe locations of low frequency ground vibrations associated with otherreceived conditioned optical signals.
 8. The system according to claim 7wherein received conditioned optical signals having an associated lowfrequency ground vibration within a predetermined distance of anon-threatening disturbance location are identified as a non-threateningdisturbance location.
 9. The system of claim 6 further comprising avibrator configured to generate low frequency ground vibrations thatmatch one or more predefined low frequency vibration patterns of the oneor more representations of prearranged optical signals.
 10. The systemof claim 9 wherein the low frequency ground vibrations are coupled tothe ground via a rod inserted into the ground.
 11. The system of claim 9wherein the low frequency ground vibrations are coupled to the groundvia a metal plate placed on a surface of the ground.
 12. The system ofclaim 9 wherein the vibrator is attached to a piece of equipment suchthat the vibrator's low frequency ground vibrations are coupled to theground where the equipment contacts the ground.
 13. The system of claim9 wherein the environmental condition variables condition the receivedoptical signal according to ground characteristics such as packed,loose, wet and dry soil at the location of the low frequency groundvibration associated with the received optical signal.
 14. A method ofidentifying a zone of non-threatening disturbances along a buriedoptical fiber comprising: inputting a light into a first end of theburied optical fiber; receiving an optical signal from the first end ofthe buried optical fiber created by a low frequency ground vibrationreceived at a location along the buried optical fiber; identifying thelocation along the buried optical fiber where the low frequency groundvibration was received; analyzing the received optical signal using anapproximation algorithm comprising: adding environmental conditionvariables to the received optical signal forming a conditioned opticalsignal; comparing the conditioned optical signal with a set ofprearranged optical signals, the prearranged optical signalscorresponding to predefined low frequency ground vibration patterns; andidentifying the low frequency ground vibration location as anon-threatening disturbance when the comparison determines that theconditioned optical signal matches one prearranged optical signal fromthe set of prearranged optical signals receiving a second optical signalfrom the first end of the buried optical fiber caused by a second lowfrequency ground vibration received at a location along the buriedoptical fiber; identifying the location along the buried optical fiberwhere the second low frequency ground vibration was received;determining whether the location of the second low frequency groundvibration is in a non-threatening disturbance zone; and identifying thesecond low frequency ground vibration as a non-threatening disturbancewhen the second low frequency ground vibration location is in anon-threatening disturbance zone.
 15. The method according to claim 14further comprising discontinuing monitoring received optical signalsfrom non-threatening disturbance zones.
 16. The method according toclaim 14 further comprising introducing a low frequency ground vibrationinto the ground using a vibrator.
 17. The method according to claim 16further comprising controlling the vibrator to produce a low frequencyground vibration signature that matches one or more of the set ofprearranged optical signals.
 18. The method according to claim 17further comprising coupling the vibrator's low frequency groundvibration signature to the ground using a rod inserted into the ground.19. The method according to claim 17 further comprising coupling thevibrator's low frequency ground vibration signature to the ground usinga metal plate placed on a surface of the ground.
 20. The methodaccording to claim 17 further comprising attaching the vibrator to apiece of equipment such that the vibrator's low frequency groundvibration signature is coupled to the ground where the equipmentcontacts the ground.
 21. The method of claim 16 wherein theenvironmental condition variables condition the received optical signalaccording to ground characteristics such as packed, loose, wet and drysoil at the location of the low frequency ground vibration.